1. Field of Invention
This invention relates generally to electronic converters adapted to change the frequency of an input signal into a corresponding digital value to provide a useful readout, and more particularly to an electronic converter of this type which consumes relatively little power and therefore may be battery operated.
2. Status of Prior Art
In certain types of flowmeters for metering the flow rate of a fluid, such as those of the positive displacement, the turbine or the vortex-shedding type, the output of the instrument is a signal whose frequency is proportional to the flow rate of the fluid being measured.
Thus, in,a vortex flowmeter such as that described in the Herzl U.S. Pat. No. 4,162,238, the presence of an obstacle in the flow conduit gives rise to periodic vortices that are sensed to produce an output signal whose frequency is a function of flow rate.
The frequencies yielded by most known types of flowmeters usually lie in a 1 to 2000 Hz range, and in the case of a vortex type meter, the output signal lies within the low end of this range. Thus, as noted in Herzl U.S. Pat. No. 4,230,391, with a vortex type meter having a six-inch diameter, the output of this meter lies in the 2 to 30 Hz range, and in another embodiment the operating range is from 3.5 Hz to 52 Hz.
In order to provide a digital readout for a meter yielding a signal whose frequency is a function of flow rate, the signal must be converted into a corresponding digital value. To convert frequency to a corresponding digital value, it is known to pass the frequency through an electronic gate which is opened for a fixed period of time, the pulse count over the gated period being indicative of the frequency.
Conventional frequency-to-digital (f to d) converters consume a substantial amount of power, and they do not, therefore, lend themselves to battery operation. The power requirements of a conventional f to d converter creates a problem where the flowmeter that yields the signal to be converted is installed at a fixed location where power lines are not available, and it becomes necessary to use battery power. In this situation, the power demand of a conventional f to d converter cannot be satisfied by batteries, for these will be exhausted in a relatively short period.